Mutations affecting the beta-subunit of bacterial tryptophan synthetase, an alpha-2 beta-2 enzyme, may influence the combining site of the subunit as well as its active site. The stability of the mutant subunit within the cell may also be affected, as well as the amount of gene product produced from adjacent genes. Such mutants will be investigated with respect to their position in the gene, their response to suppressor mutations, and their primary and quaternary structural aberrations. Their ability to combine with and complement "repairable" beta-chain mutants will also be determined as an independent indication of conformational damage. Comparative studies of the primary structure and mode of regulation of the enzyme in disparate bacterial groups, especially Pseudomonas and Acinetobacter, will augment these studies and determine which conclusions can be generalized to any bacterial tryptophan synthetase and which are particular to Escherichia coli and the enteric bacteria. Intergroup hybrid molecules formed in vitro will be studied to determine the evolutionary conservation of supportive sites of interaction. Several other bacterial groups about whose tryptophan enzymes little or nothing is known will be explored for comparisons of regulation and enzyme structure. BIBLIOGRAPHIC REFERENCES: Regulation of enzyme synthesis in the tryptophan pathway of Acinetobacter calcoaceticus, W. Cohn and I. P. Crawford, J. Bacteriol. 127, 367-379 (1976). Evidence for autogenous regulation of Pseudomonas putida tryptophan synthase, A. R. Proctor and I. P. Crawford, J. Bacteriol. 126, 547-549 (1976).